Most theories today posit that dopamine encodes the positive predictive error between a true reward and an expected reward. So if the reward is much more than you expect lots of dopamine will be released, but if it is exactly what you expected then none will be released. Dopamine enhances the experience of the reward by lowering the rate of firing required in the reward area to experience the same reward in the absence of dopamine. Thus, lesser rewards feel better when there is differential expectation. So dopamine enhances the feeling that's already there.

I think the difference is that neurochemicals can alter your mental state, which affects other feelings and decisions. But being happy about getting a problem resolved doesn't "leak" in the same way.